Follicles were collected from ovaries removed under halothane anaesthesia from 7 rhesus monkeys. Follicle and ovum diameters were measured and chromatin organization was determined by fluorescence microscopy. Growth curves of follicle size in relation to ovum size showed that the ovum diameter increased rapidly to 90 u in proportion to an increase in follicle diameter to 200 u. Thereafter, the ovum growth slowed (from 90 to 110 u) in relation to follicle growth (from 200 to 8000 u). Chromatin organization progressed in relation to ovum size. The relationship of follicle and oocyte growth and perinucleolar chromatin configuration is being analyzed with reference to stage of the menstrual cycle.